Quadruplex amplifier



p 1931. E. A. WILLSON ET AL 1,821,490

QUADRUPLEX AMPLIFIER Filed Oct. 2, 1929 2 Sheets-Sheet l ETl-ELRED ALFRED WILLSON HAMD FRANK WODMAN DALE GREG I INVENTORS BY fwd. 7 f6. k

ATTORN QUADEUPLEX AMPLIFIER 2 she ts sheezl 2 Filed Oct. 2. 1329 FIG.

M m n N m y m L Q m m m fi w a u 7 1 m w v: .n m. -1 M Tw fl n m ETHELRED ALFRED WILLSON HAROLD FRANK WOODMAN EMILE GREIG Patented Sept. 1, 1931 ETHEL RED ALFRED WILLSON, HAROLD F CROYDON, ENGLAND, ASSIGNOBS TO GBEED ENGLAND AND LIMITEDQOI' GROYDON,

onannvrnnx mums Application filed October 2, 1829, Serial Ro l 396,825, and in Great Britain November 2, 1928.

As is well known the selective geception of telegraphic signals transmitted in ac cordance with the quadruplex system of telegraphy is commonly effected with the aid of selective relays, that is to say, the so-called A signals are selected according to their signs by a. polarized rela while the so-called B signals are selecte according to their magnitude by a nonpolarized relay so arranged that the A signals are of 1nsufficient magnitude to actuate it.

It is an object of the present invention to provide means for the selective amplification of signal impulses received in quadruplex telegraphy.

As the invention concerns only the receiving arrangements for the discrimination between the different signals, it is equally applicable to receiving si nals on tlie diplex system. It will be un erstood therefore that all references to quadruplex must be taken as equally applicable to diplex telegraphy, and vice versa.

In accordance with the invention incoming superposed A and B signal impulses of a quadruplex telegraph system are applied, with or without previous amplification common to both sets of impulses, simultaneously to two thermionic valve systems each associated with recording or reproducing means, whereof the one valve system is'responsive to changes of signal polarity but unresponsive to potential changes'greater 1n amplitude than those due to A signals, while the other valve system is unresponsive to potentials due to A signalsbut responsive to potentials due to B signals irrespective of their sign.

It is also known that in quadruplex telegraphy the B signals suffer mutilation owing to effect of the reversals brought about by the A signals. More explicitly stated, these reversals of polarity are not instantaneous,

but occupy a certain amount of time, so-

that when a number of. A signal reversals coincide with a long B signal the latter becomes split up.

It is a further object of the present invention to overcome this difiiculty and to this end the marking and the spacing cur- 1mm: WOQDMAN, nn Emu: GREIG, or

rents actuating the B signal relay are, ac-

cording to-the'invention, subjected to a relative displacement of phase so adjusted that;

points of spurious interruption of the received B signal are bridged over and irregularities obliterated in the combined efl'ect of the two out of phase currents on the B signal recording or reproducing means. In practice the desired phase displacement mayhe' efiected for instance, by the use of a phasing condenser or condensers connected across one of the relay coils.

In order that the invention may more readily be understood and carried into practice, reference is made hereinafter to the accompanying drawings Fig. 1 is a circuitdiagram showing a bridge circuit for telegraphic transmission and reception in association with a quadruplex amplifying and selective reproducing or repeating circuit in accordance with the invention.

Fig. 2 is a diagram showing the shapes of certain transmitted and received signals and serves to illustrate the'method adopted, according to the invention, for improving the selective reception of B signals.

Referring first to Fig. 1, the circuit connectiondesignated generally by the reference character C will be recognized, by those skilled in the art, as the well known bridge circuit, to which the cable loop L and arti-' ficial loop L? as well as the transmitter X are connected in the usual manner. The transmitter X comprises two transmitters and shaping inductance 7', while 0 is the reading condenser (with resistance shunt) conconnected in the usual manner, one for angnected in series with one of the two reslstances 1", r across WhlCh the receiving apparatus is connectedin the-mannerhereinafter to be described.

The potentials developed across 1' and r are ap lied differentially to the amplifier, for Whlch purpose the junction 70 is directly connected to the negative lead Z of said amplifier while the terminals n and '0 are connected through similar grid biasing devices b and b to the grids of a pair of valves 2 and 22 which are of like characteristic and which operate under like conditions as amplifiers of the combined incoming A and B signals. 1' and r are the anode resistances for these valves which. in common with all the other valves of the amplifier, derive their anode potential from a high tension source H. The auxiliary anode resistances p and p act in the capacity of potentiometer-s for adjustment of the grid potentials of the battery coupled valves, hereinafter referred to, in which the A and B signals are resolved.

Inasmuch as the A signals are defined by mere reversals of polarity it is immaterial whether, for the resolution and further amplification of these signals, the output be taken from valve 2 or from valve 22. In the example illustrated the adjustable contact of the potentiometer 79 is connected through a coupling battery I) to the grid of a valve 3, the mean grid potential of this valve being so adjusted that the negative A signal reduces the grid potential to a point at the bottom bend of the characteristic (anode current-grid voltage) curve for the valve in question while a positive A signal brings the grid potential to a point on the slope of the characteristic or, it may be (in the case of a valve with a very short grid voltage swing) to the saturation point. The result of selecting andnsing the valve 3 in the manner indicated is that such valve acts perfectly as an amplifier for the A signals but is more or less indifierent to the potential changes of much greater amplitude set up by the B signals. Considering the case of negative signal potentials impressed'on the grid of the valve 3, it will be clear that if negative A signals reduce the grid voltage to the bottom bend of the characteristic, any further reduction of grid voltage, due to a B signal applied in the negative sense. will bring about no appreciable change in the anode current of the valve. even though the potential changes due to the B signals may have (as is usual) three times the amplitude of the potential changes due to A signals alone. Thus B signals received in the negative sense may be regarded as being cut oil at the amplifying valve 3 and a somewhat similar cut-off of positive B signals may be obtained either at the top end of the same valve (if the A signal amplitude occupies the whole of the straight part of the characteristic) or at the bottom bend of a succeeding coupled valve 4, the latter expedient being preferable, for reasons which will be obvious, having regard to the characteristics of modern amplifying valves. For these same reasons, as well as with a view to obtaining a high degree of amplification it is. preferable not to insert the 130-- larized relay for the A signals directly in the anode circuit of valve 3 but, rather to employ the further valves 4 and 5 in the anode circuits of which the marking and spacing coils A and A of the A signal relay are respectively connected.

r is the anode resistance for valve 3 and b the coupling battery while the auxiliary adjustable anode resistance p permits the grid potential of the valve 45 to be so adjusted as to produce a bottom bend cut-oil effect at a potential corresponding to a positive A signal, whereby still more positive B signal potentials are prevented from pro ducing any effect in. the anode circuit of the valve 4, the negative B signal having already been cut off in the valve 3, as above described."

The-marking coil A of the polarized relay is included in the anode circuit of the valve 4, which circuit also includes an anode resistance r and b is a coupling battery for the grid of the valve 5 having the spacing coil A in its anode circuit. The valve 5 is biased to work on the straight part of its characteristic, its mean grid potential not being critical within a few volts.

For the resolution of B signals the inven tion employs thermionic valves in such a manner that the A signals are of insufiicient amplitude to produce any change of anode current and only the B signals can do this. Also. since the B signals are, incidently. subject to changes of polarity, brought about by the presence of A signals on the line the B signal selective system must function irrespective of such changes.

As shown in the drawings. the B signal selecting and amplifying system comprises a pair of valves 6 and 66 having their anodes connected together. so that their plate filament paths are in parallel and their grids coupled respectively (through coupling batteries 1) and b and the potentiometers p and p to the anodes of the valves 2 and 22. The grid bias of these paralleled valves 6 and 66 is so adjusted that the highest absolute potential which the grid of either of them can possibly acquire under the influence of A signals lies on or to the left of the bottom bend of the characteristic and, therefore, cannot produce any change of anode current. 011 the other hand, B signals applied in the positive sense to the grid of either valve will raise the grid voltage to a value corresponding to a point well up in the straight part of the characteristic curve, thus producing a relatively large anode current. Of course, neither valve will when biased as above mentioned, respond to decreases of grid potential. It must be remembered, however, that the incoming signals are applied differentially to the amplifying valves 2 and 22, so that at any given instant when the grid of one of thesevalves is becomingmore negative the grid of the other is becoming more positive. Thus the anode current in one will be decreasing when the anode current in the other is increasing. The potentials at the moving contacts of the -po tentiometers p and 12 will therefore vary about a mean value in differential relations to each other, one becoming positive when the other is negative, and these differential potential variations will, of course, be transferred, through the coupling batteries b and'bto the grids of the valves 6 and 66. Thus if the grid potential of valve 6 drops below the mean value under signal influence of the A signal transmitter (that is to say,

whether the A signal key happens to be in the up or in the down position). Other wise stated, the impedance of the joint platefilament paths of the two valves-6 and 66 is always reduced whenever B signals are received and irrespective of any polarity changes due to the A signals. 1' is the common anode resistance for the paralleled valves 6 and 66, while 6 is a coupling battery and 1 a variable resistance for adjusting the mean potential applied to the grid of the valve 7 in the anode circuit of which is the spacing coil B of the non polarized relay for the B signals. The marking coil B for this same relay is in the anode circuit of the valve 8 which, with the aid of anode resistance 1' and coupling battery 6 is coupled to the valve 8. To overcome the effect of the B kick there is shown in Fig. 1 a phase-splitting device, consisting in this case of a condenser c which is connected in shunt with the winding B'. This condenser serves to bring about a phase difl'erence as between the spacing current in B and the marking current in B, thereby bridging over (as it were) the gaps in the long B signals, when the two out-of-phase currents take effect additively in therelay to control the tongue thereof.

The effect of thus throwing the marking and spacing currents out of phase will more clearly be understood on reference to Fig. 2 of the drawings.

In Diagram I of this figure the transmitted A signals are shown as a sequence of reversals, while Diagram II shows a simultaneously transmitted B signal, in this instance, a short mark, a space and a long mark (Morse a, for instance). The effect of combining the A and B signals in transmission is shown at III, in which diagram it is assumed that the reversals of the transmittedsignal current take place in synchronism with the reversals of the A signals, while the amplitude attained at each reversal depends entirely on the presence or absence ofB'signal elements. When B signal marking impulses are on the line the amplitude attained after each reversal is in practice, about three times that due to A signals alone.

The combined effect of the relay transit times and the unavoidable distortion of the signals due to the KR of the line accounts for the loss of a proportion of the marking time at each reversal so that the received composite signal impulses (i. e. the signals arriving at the receiver) have a form somewhat as illustrated in Diagram IV in which the lines and 3/ show the current value to which the relay, energized by the'Bj signals, -wi ll respond in the positive -and negative senses respectively. This shows that instead of the reversals being instantaneous, a time, indicated for convenience by the distance T on the diagram, will be occupied in bringing about a change from the operating positive current to that in the negative direction.

When the. B signals are resolved by the .aid of the. valves 6 and 66 (Fig. 1) the output from valve 7 will present an appearance somewhat as shown in Diagram Vm and this might be regarded as representing marking current for the B signal relay. It will be seen, that the reversal of the incoming impulses has resulted in the long B signal marking impulse being split up into three separate short impulses with spaces in between. If the B signal relay is ordinarily sensitive its tongue will attempt to respond to these fluctuations or gaps in the long signal so that the relay will be unstable and the marking inaccurate if the currents in both coils of the relay are substantially in phase. Diagram V indicates however, a marking current on (in the winding B) and a spacing current 8, showing the same fluctuations as the marking current but operating in the winding B and leading the marking current, in point by phase, by an amount the value of which should be adjusted to suit the length of the B kick in proportion to the rest of the signal unit of time. In practice the phase displacement may amount to 9095% of the time of one marking unit impulse and thus the phase relationship between and s is such that an overlap t exists as between each marking period of the marking current m and the corresponding zero period of the spacing current 8.

It should here be explained. with reference to Diagram V that the marking current fiuctuates from zero to a maximum value indicated by the line M and that the spacing current fluctuates from zero to a maximum value indicated by line S. 4

The combined effect of the currents m and s on the tongue of the B relay is shown in Diagram VII of Fig. 2. The reason for this is apparent, if the instantaneous values of m and s in Diagram V be added algebraically starting from the left of the diagram and from a given time datum line If and plotted against time as in Diagram VI. m and s commence at zero marking and maximum spacing respectively, the relay tongue being on its spacing contact. After a short time s falls to zero without affecting the relay tongue, and the effective relay operating the current remains at zero until m rises its maximum value M and moves the tongue to the marking contact. After another brief interval t (the amount of the overlap aforesaid) the spacing current rises to its maximum value S. The instantaneous values of m and s are now equal and opposite so the relay tongue continues to mark until, at the end of one marking unit impulse, the marking current m drops back to zero and permits the spacing current 8. which is still at its maximum value S, to move the relay tongue to the spacing position. When the spacing current s is reduced to zero after a short interval the relay tongue is again unaffected asfthe marking current is also at zero, but on the increase of the marking current again, the relay starts to mark.

Continuing the addition of the currents m and s, it will readily be apparent that the gaps or interruptions in the long signal become obliterated in the process, the actual movements of the relay tongue being such as to reproduce the original B signal of Diagram H in the form shown in Diagram VII, in which the signal form is correct excepting for slight exaggerations of the spacing.

What is claimed is:

1. Apparatus for the selective reproduction of telegraphic signals, comprising two thermionic valves, each having an input and an output circuit, means for applying signals to the input circuit of one of said valves, a connection from the output circuit of said valve to the input circuit of the other valve, a reproducing relay having two windings and placed in the respective output circuits of the two valves and a condenser connected in parallel to one of said windings for causing a phase shift of a portion of the applied signals.

2. Apparatus for the selective reproduction of telegraphic signals represented by changes of signal polarity comprising a therefor, means for biasing said valve so that signals of one polarity will not produce more than a predetermined change in output current, a second thermionic valve, input and output circuits therefor, a connection between its input circuit and the output circuit of the first said valve means for biasing said second valve so that signals of the other polarity applied to the input circuit of the first said valve will not produce more than a predetermined change in current in the output circuit of the secondvalve, and signal reproducing means connected to the output circuit of the said second valve.

.3. Apparatus for the selective reproduction of telegraphic signals comprising an input circuit, means for applying signals thereto, two thermionic valves connected difi'erentially to the said receiving circuit, separate output circuits therefor, two other thermionic valves having separate input circuits connected to the respective output circuits of the other said valves and a common output circuit, and signal reproducing means connected to the said common output circuit.

*1. Apparatus for the selective reproduc-.

tion of telegraph signals comprising two thermionic valves, each having an input and an output circuit, means for applying signals to the input circuit of one of said valves, a connection from the output circuit of said valve to the input circuit of the other valve, means in the output circuit of one of said valves for displacing the phase of the currents therein relative to the currents in the output circuit of the other of said valves, and a nop-polarized reproducing relay having a winding in each of said output circuits.

5. Apparatus for selectively and separately reproducing signals in diplex telegraphy comprising an input circuit, means for applying signals thereto, two thermionic valve systems connected to the said input circuit, means for separately biasing the two systems that changes in input potential below a predetermined magnitude will have no effect on the one system and changes in input potential above a certain magnitude will haveno effect on the other system, separate output circuits for the two systems and signal reproducing means in each output circuit.

6, In a quadruplex telegraph system, means for transmitting impulses of currents of opposite polarity, means for increasing and decreasing said currents, a polarized relay responsive to the reversals of polarity of the normal current, a non-polarized relay responsive only to said increased or decreased currents whatever their polarity and having two windings in two separate cirthermionic valve, input and output circuit' cuits, means for impressing signals on both LUZ) said circuits, and means for shifting the phase of the currents in one of said 011- cuits relative to the other.

7. In a quadruplex telegraph systemi a line, a signal receiving circuit connecte thereto, a pair of thermionic valves having their grids connected to opposite ends of said receivingcircuit and one end of both the filaments connected to the middle point of said receiving circuit, output circuits .for

each of said valves, a connection between a point in one of said output circuits and the grid of another valve so biased that changes of input potential greater than a predetermined value produce no effect, A. signal reproducing means connected to the output circuit of said last mentioned valve, a connection between a point in the output circuit of each of said first mentioned valves and the grids of two other valves so biased that changes of input potential less than a predetermined valve produce no effect, a common output circuit for the last-mentioned valves, and B signal reproducing 2 means connected thereto.

8. In a quadruplex telegraph system, apparatus for the selective reproduction of telegraphic signals comprising a pair of thermionic valve circuits having a common input circuit, the valves in one of said circuits being biased to permit the passage of signals of varying polarity, the valves in the other of said circuits being biased to permit the passage of signals of varying potential and reproducing means in the out put of each of said circuits.

9. In a quadruplex telegraph system, apparatus for the selective reproduction of telegraphic signals comprising a pair of thermionic valve circuits having a common input circuit, each of said valve circuits being adjusted to permit the passage of a certain predetermined portion of a composite signal, reproducing means in the output of each of said circuits and phase shifting means associated with one of said reproducing means for neutralizing disturbances arising in said common input circuit.

In witness whereof We hereunto subscribe our names this sixteenth day of September,

ETHELRED ALFRED WILLSON. HAROLD FRANK WOODMAN.

EMILE GREIG. 

